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This patch does not remove all occurrences of the words in question. Rather, I went through all of the occurrences of the words listed below, and judged if they a) suggested the reader had some kind of knowledge/experience, and b) if they added anything of value (including tone of voice, etc). I left most of the words alone. I looked at the following words: - simply/simple - easy/easier/easiest - obvious - just - merely - straightforward - ridiculous Thanks to Carlton Gibson for guidance on how to approach this issue, and to Tim Bell for providing the idea. But the enormous lion's share of thanks go to Adam Johnson for his patient and helpful review.
184 lines
6.1 KiB
Plaintext
184 lines
6.1 KiB
Plaintext
==============
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Managing files
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==============
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This document describes Django's file access APIs for files such as those
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uploaded by a user. The lower level APIs are general enough that you could use
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them for other purposes. If you want to handle "static files" (JS, CSS, etc.),
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see :doc:`/howto/static-files/index`.
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By default, Django stores files locally, using the :setting:`MEDIA_ROOT` and
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:setting:`MEDIA_URL` settings. The examples below assume that you're using these
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defaults.
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However, Django provides ways to write custom `file storage systems`_ that
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allow you to completely customize where and how Django stores files. The
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second half of this document describes how these storage systems work.
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.. _file storage systems: `File storage`_
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Using files in models
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=====================
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When you use a :class:`~django.db.models.FileField` or
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:class:`~django.db.models.ImageField`, Django provides a set of APIs you can use
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to deal with that file.
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Consider the following model, using an :class:`~django.db.models.ImageField` to
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store a photo::
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from django.db import models
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class Car(models.Model):
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name = models.CharField(max_length=255)
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price = models.DecimalField(max_digits=5, decimal_places=2)
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photo = models.ImageField(upload_to='cars')
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Any ``Car`` instance will have a ``photo`` attribute that you can use to get at
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the details of the attached photo::
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>>> car = Car.objects.get(name="57 Chevy")
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>>> car.photo
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<ImageFieldFile: chevy.jpg>
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>>> car.photo.name
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'cars/chevy.jpg'
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>>> car.photo.path
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'/media/cars/chevy.jpg'
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>>> car.photo.url
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'http://media.example.com/cars/chevy.jpg'
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This object -- ``car.photo`` in the example -- is a ``File`` object, which means
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it has all the methods and attributes described below.
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.. note::
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The file is saved as part of saving the model in the database, so the actual
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file name used on disk cannot be relied on until after the model has been
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saved.
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For example, you can change the file name by setting the file's
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:attr:`~django.core.files.File.name` to a path relative to the file storage's
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location (:setting:`MEDIA_ROOT` if you are using the default
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:class:`~django.core.files.storage.FileSystemStorage`)::
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>>> import os
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>>> from django.conf import settings
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>>> initial_path = car.photo.path
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>>> car.photo.name = 'cars/chevy_ii.jpg'
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>>> new_path = settings.MEDIA_ROOT + car.photo.name
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>>> # Move the file on the filesystem
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>>> os.rename(initial_path, new_path)
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>>> car.save()
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>>> car.photo.path
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'/media/cars/chevy_ii.jpg'
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>>> car.photo.path == new_path
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True
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The ``File`` object
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===================
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Internally, Django uses a :class:`django.core.files.File` instance any time it
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needs to represent a file.
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Most of the time you'll use a ``File`` that Django's given you (i.e. a file
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attached to a model as above, or perhaps an uploaded file).
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If you need to construct a ``File`` yourself, the easiest way is to create one
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using a Python built-in ``file`` object::
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>>> from django.core.files import File
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# Create a Python file object using open()
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>>> f = open('/path/to/hello.world', 'w')
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>>> myfile = File(f)
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Now you can use any of the documented attributes and methods
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of the :class:`~django.core.files.File` class.
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Be aware that files created in this way are not automatically closed.
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The following approach may be used to close files automatically::
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>>> from django.core.files import File
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# Create a Python file object using open() and the with statement
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>>> with open('/path/to/hello.world', 'w') as f:
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... myfile = File(f)
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... myfile.write('Hello World')
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...
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>>> myfile.closed
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True
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>>> f.closed
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True
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Closing files is especially important when accessing file fields in a loop
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over a large number of objects. If files are not manually closed after
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accessing them, the risk of running out of file descriptors may arise. This
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may lead to the following error::
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OSError: [Errno 24] Too many open files
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File storage
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============
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Behind the scenes, Django delegates decisions about how and where to store files
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to a file storage system. This is the object that actually understands things
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like file systems, opening and reading files, etc.
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Django's default file storage is given by the :setting:`DEFAULT_FILE_STORAGE`
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setting; if you don't explicitly provide a storage system, this is the one that
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will be used.
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See below for details of the built-in default file storage system, and see
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:doc:`/howto/custom-file-storage` for information on writing your own file
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storage system.
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Storage objects
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---------------
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Though most of the time you'll want to use a ``File`` object (which delegates to
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the proper storage for that file), you can use file storage systems directly.
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You can create an instance of some custom file storage class, or -- often more
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useful -- you can use the global default storage system::
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>>> from django.core.files.base import ContentFile
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>>> from django.core.files.storage import default_storage
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>>> path = default_storage.save('path/to/file', ContentFile(b'new content'))
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>>> path
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'path/to/file'
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>>> default_storage.size(path)
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11
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>>> default_storage.open(path).read()
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b'new content'
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>>> default_storage.delete(path)
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>>> default_storage.exists(path)
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False
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See :doc:`/ref/files/storage` for the file storage API.
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.. _builtin-fs-storage:
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The built-in filesystem storage class
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-------------------------------------
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Django ships with a :class:`django.core.files.storage.FileSystemStorage` class
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which implements basic local filesystem file storage.
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For example, the following code will store uploaded files under
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``/media/photos`` regardless of what your :setting:`MEDIA_ROOT` setting is::
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from django.core.files.storage import FileSystemStorage
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from django.db import models
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fs = FileSystemStorage(location='/media/photos')
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class Car(models.Model):
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...
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photo = models.ImageField(storage=fs)
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:doc:`Custom storage systems </howto/custom-file-storage>` work the same way:
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you can pass them in as the ``storage`` argument to a
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:class:`~django.db.models.FileField`.
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